In this article, a novel microstrip patch antenna of size 210 × 205 × 22 μm3 operating in the terahertz band is proposed. We then perform optimization of the proposed antenna using the Golden Ratio technique to realize an antenna with reduced dimensions and better performance. The optimized nanoantenna has reduced dimensions of 120 × 160 × 14 μm3 (≈ 71.61 % reduction in volume); improved return loss S11 ( 5.29 dBi), and bandwidth (156.9 GHz i.e., 45% more). The results are validated through an equivalent circuit model (ECM) in Advanced Design System (ADS), demonstrating good agreement with the CST Studio results. Next, a human heart-phantom model has been created and tested for each designed scenario. It examines the interactions between the heart tissues and the proposed antenna, and it identifies the substrate material that performs the best. The results show that polytetrafluoroethylene (PTFE) material performs better than other substrates. Additionally, the research includes an analysis of the link budget of terahertz channels in the intrabody nanocommunication networks—a bio-medical application. The findings indicate the feasibility of using nanoantennas for practical in-vivo nanocommunications.